Proposals have already been made on numerous occasions to use EPDM-based elastomers cured by organic peroxides in the manufacture of power transmission belts, because of the qualities and advantages of such elastomers such as cost, operating temperature range, and ability to withstand oxygen and ozone, such EPDM-based elastomers having additives which improve their dynamic properties such as resistance to fatigue and to wear, their breaking strength, and their modulus of elasticity, and also their adhesion to traction cords, which additives are generally constituted by metallic salts of .alpha.,.beta.-unsaturated organic acids (in particular zinc methacrylate) plus reinforcing fillers such as carbon black and possibly fibers, e.g. aramid fibers.